LM 12 installed in dual boot configuration with functioning W7. However, although W7 appears in the selection screen it won't boot from there.
I've followed the advise in the LXF 133 page 44 Troubleshooting FAQ as part of Perfecting multi-booting topic re this very issue - and it doesn't help. Are the details of that article all correct?

I have W7 is at /dev/sdb1 and LM12 at/edv/sdb5. What do I need to do to get W7 booting?

Booting W7 and ... ? I have found some linux flavours dont play nicely, but most can be easily fixed.

Do you get a menu to choose from ?

Try boot into linux. edit /boot/grub/grub.cfg (I can hear pitch forks a-comming...)
Find your W7 entry and try changing up or down a disk number and see if that works. I've found that the numbers/letters are sometimes misleading, depending on what OS is reading them at what time.